If the power lines in your building are heavily polluted with electrical noise, a separate ground connection may reduce the background noise level. You should think about such measures if an "empty" measurement with unpowered DUT shows already a high level near the limit values.
The metal sheet and LISN ground will be normally connected to the regular protective earth.
If the power lines in your building are heavily polluted with electrical noise, a separate ground connection may reduce the background noise level. You should think about such measures if an "empty" measurement with unpowered DUT shows already a high level near the limit values.